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Dopamine can be found in the peel and fruit pulp of bananas. Many plants, including a variety of food plants, synthesize dopamine to varying degrees. [145] The highest concentrations have been observed in bananas—the fruit pulp of red and yellow bananas contains dopamine at levels of 40 to 50 parts per million by weight. [145]
l-DOPA is the precursor to the neurotransmitters dopamine, norepinephrine (noradrenaline), and epinephrine (adrenaline), which are collectively known as catecholamines. Furthermore, l -DOPA itself mediates neurotrophic factor release by the brain and CNS.
Tyrosine hydroxylase or tyrosine 3-monooxygenase is the enzyme responsible for catalyzing the conversion of the amino acid L-tyrosine to L-3,4-dihydroxyphenylalanine (L-DOPA). [5] [6] It does so using molecular oxygen (O 2), as well as iron (Fe 2+) and tetrahydrobiopterin as cofactors.
Fibroblast growth factor 21 (FGF-21) is a protein that in mammals is encoded by the FGF21 gene. [ 5 ] [ 6 ] The protein encoded by this gene is a member of the fibroblast growth factor (FGF) family and specifically a member of the endocrine subfamily which includes FGF23 and FGF15/19.
A growth factor is a naturally occurring substance capable of stimulating cell proliferation, wound healing, and occasionally cellular differentiation. [1] Usually it is a secreted protein or a steroid hormone .
Genentech pioneered the use of recombinant human growth hormone for human therapy, which was approved by the FDA in 1985. [citation needed] Prior to its production by recombinant DNA technology, growth hormone used to treat deficiencies was extracted from the pituitary glands of cadavers. Attempts to create a wholly synthetic HGH failed.
In the brain, serotonin is a neurotransmitter and regulates arousal, behavior, sleep, and mood, among other things. [9] During prolonged exercise where central nervous system fatigue is present, serotonin levels in the brain are higher than normal physiological conditions; these higher levels can increase perceptions of effort and peripheral muscle fatigue. [9]
Prolactin and its receptor are expressed in the skin, specifically in the hair follicles, where they regulate hair growth and moulting in an autocrine fashion. [29] [30] Elevated levels of prolactin can inhibit hair growth, [31] and knock-out mutations in the prolactin gene cause increased hair length in cattle [32] and mice. [30]